Clauses 4, 5 and 6 of this part of IEC 61992 cover particular requirements for surge arresters (following named arresters) for specific use in fixed installations of d.c. traction systems. These are surge arresters consisting of one or more non-linear resistors which may be in series with single or multiple spark gaps. Low-voltage limiters are covered under Clause 7. These are protective devices mainly used in fixed installations of d.c. traction systems to connect certain portions of the circuit, when, owing to an abnormal situation, the voltage across the device exceeds a predetermined limited value. They may be associated with other devices such as contactors for self-restoring arrangements. They are not used in general to provide surge protection. The following are the main uses of Low-Voltage Limiters (LVL): – connection to the rail of metallic masses; – protection of rail circuits; – earthing of rails in the substation; – protection of cathodic circuits; – protection of cable shields.